Strontium-82/rubidium-82 biomedical generators are used for cardiovascular imaging applications. Rubidium-82 is the daughter of strontium-82 and is the radionuclide used in the cardiovascular imaging. The strontium-82 is produced through the irradiation of materials such as molybdenum or rubidium in particle accelerators. This process is expensive and requires unique facilities that are not always available.
The strontium-82 activity has then been recovered from the irradiated materials by chemical processing such as described in U.S. Pat. Nos. 3,957,945, 4,276,267, and 5,167,938. The earlier patents described processes involving the use of one or more organic solvents for the selective separation of the strontium. The later patent eliminated the need for organic solvents in the separation thereby eliminating a mixed hazardous waste product.
The strontium-82 from such processing is incorporated into strontium-82/rubidium-82 biomedical generators such as described in U.S. Pat. Nos. 4,406,877 and 4,597,951. Such generators generally include a housing (or column) for containing a support medium for the parent radionuclide, an inlet for introducing an eluant into the housing, and an outlet for withdrawing the eluted radionuclide from the housing. Such generators lose their potency over time as the parent radionuclide decays and eventually the generators are discarded. Such spent generators are themselves a radioactive waste stream with the associated costs. At this time, there are fourteen clinics in the United States using strontium-82/rubidium-82 biomedical generators distributed under the trade name CardioGen.RTM. generators. Each generator is initially produced with a strontium-82 loading of about 100 milliCuries. Each generator is then used for one month at which time there are about 50 milliCuries of strontium-82 remaining. After a month, the generator is considered used or spent. The present procedure has been to supply a new generator to each clinic, each month and to collect the used generator for disposal as waste.
As rubidium-82 has become more widely used for cardiovascular imaging, its regular, continual availability and supply have become essential. Periods of prolonged shutdowns of the few facilities capable of producing strontium-82 could threaten the supply of this needed radioisotope to produce the strontium-82/rubidium-82 biomedical generators. Alternative sources of irradiated targets have been investigated and targets from accelerators in Russia have now been used to supply or supplement the needed strontium-82 during periods of time when sources in the United States are not available. Yet, the concern for possible loss of irradiated targets for prolonged periods of time has maintained concerns for alternative sources of strontium-82.
During the present inventors' search for alternative sources, they have now investigated the recovery of strontium-82 activity from the spent strontium-82/rubidium-82 generators. Recovery of such strontium-82 activity from the spent generators could serve as an alternative source of strontium-82, while reducing the overall waste stream from the use of such biomedical generators.
It is an object of this invention to provide a technique to recover strontium radioisotopes from generators that are no longer useful due to low potency, and use the recovered material to produce new generators.
Another object of the present invention is to produce material (i.e., strontium-82) to manufacture generators at reduced cost without the need for accelerator irradiations.
Still another object of the present invention is to minimize what has previously been a radioactive waste stream and convert at least a portion of it into a useful product by recycling strontium activity from spent strontium-82/rubidium-82 biomedical generators.